Pentair 250, 300 installation manual Operation of Ignition Module

Basic Operation 22

SAFETY CONTROLS, (cont’d.)

IGNITION MODULE

The Ignition Module is microprocessor based and operates on 24 VAC supplied by the transformer. The control utilizes a microprocessor to continually and safely monitor, analyze, and control the proper operation of the gas burners. The module with the presence of the flame sensor/ignitor or remote sensor, using flame rectification, allows the heater to operate.

HIGH LIMITS

A “High Limit”, is a safety device that opens the electrical circuit and shuts off the heater based on a temperature set point within the “High Limit Device”. The MiniMax NT Low NOx series of heaters contains three (3) high limit devices, two (2) are located on the main inlet / outlet header, one sensing the inlet water temperature and one sensing the outlet water temperature. The third high limit is located on the exhaust outlet and senses the temperature of the flue gas.

OPERATION OF IGNITION MODULE

HEAT MODE

•When a call for heat is received from the thermostat supplying 24 VAC to the “W” module terminal, the control will perform a self check routine, flash the diagnostic LED, on units manufactured prior to

10-15-01,(located on the module) for up to four seconds and begins the safety timing ignition sequence. After the fan prepurge cycle, the hot surface ignitor is activated for a heat-up period followed by energization of the gas valve for the trial for ignition period.

•When flame is detected during the trial for ignition, the ignitor is deactivated and the gas valve remains energized. The thermostat and main burner flame are constantly monitored to assure the system continues to operate properly. When the thermostat is satisfied and the demand for heat ends, the main valve is de-energized immediately.

FAILURE TO LIGHT-LOCK OUT

Should the main burner fail to light, or flame is not detected during the trial for ignition period, the control will go into lockout and the gas valve will be turned off immediately. The thermostat controller will display a flame failure error (icon/service LED) and recovery from lockout requires a manual reset by either resetting the 7800 Thermostat or removing 24 VAC from the system by turning off main power switch (located on the junction box behind right door) for a period of 5 seconds.

FLAME FAILURE—RE-IGNITION

If the established flame signal is lost while the burner is operating, the control will respond within 1 second. The gas valve is de-energized and the control starts a new ignition sequence in an attempt to relight the burner. If the burner does not relight, the control will go into lockout, requiring a manual reset.

P/N 471593 Rev. C 11-1-01